1. Field of the Invention
This invention relates to a method of depositing nitrogen-doped beta tantalum and more particularly, to a method of depositing nitrogen-doped beta tantalum films for fabricating nitrogen-doped beta tantalum capacitors.
2. Description of the Prior Art
Electronic systems, particularly those in the communications industry, are rapidly becoming larger and more complex. With the development of increasingly more complicated electronic systems, the number of circuit components and necessary interconnections has increased many times over. The failure of even one component or of one lead connection can mean the failure of an entire system and an accompanying loss of service. Accordingly, components and interconnection techniques meeting reliability requirements of small systems may not be sufficiently reliable when connected in vast quantities in large, modern electronic systems.
Extensive research effort has been directed toward producing circuits and circuit elements which are reliable and stable in use and retain these characteristics over prolonged life periods. Tantalum integrated thin-film circuitry technology has evolved in response to this need.
Utilization of the thin-film technology inherently permits a substantial reduction in individual lead connections with accompanying increase in reliability. This reduction in individual lead connections is possible because a plurality of circuit components can frequently be formed on a single substrate from a single continuous film or from adjacent film layers inherently interconnecting the components. If the circuit components thus interconnected have the required reliability and stability, highly reliable and stable electronic systems can be built in this manner.
The stability and reliability of thin-film circuit components and therefore thin-film circuits depend to a considerable extent upon the material used to form the thin films. For this reason, there is a great need to find new materials for forming improved thin-film circuit elements. One such new material is beta tantalum which is revealed and described in U.S. Pat. No. 3,382,053, assigned to the assignee hereof and Bell Telephone Laboratories, Inc., and incorporated by reference hereinto and in U.S. Pat. No. 3,275,915, assigned to the assignee hereof and also incorporated by reference hereinto.
Pure beta tantalum is an excellent material for both thin-film capacitors and resistors. It has been found that another new material, nitrogen-doped beta tantalum permits even further improvement in tantalum thin-film component stability and reliability.
Nitrogen doping of beta tantalum refers to combining nitrogen atoms with tantalum atoms to form a beta tantalum crystalline structure having the nitrogen atoms interstitially incorporated therewith or therein. It had been previously thought that depositing tantalum, under conditions whereby beta tantalum forms, in the presence of nitrogen atoms, present in even small quantities, i.e., nitrogen doping of the resultant tantalum deposit, caused the resultant deposited tantalum to transform from the beta tantalum crystalline phase to the body-centered cubic structure of bulk or .alpha. tantalum, with an accompanying drop in resistivity. However, it has been surprisingly found that such is not true and that nitrogen doping of beta tantalum can be carried out without changing the crystal structure of beta tantalum to body-centered cubic and without forming other tantalum-nitrogen compounds of distinct crystalline structure such as Ta.sub.2 N (hexagonal close packed) or TaN (sodium chloride structure). It has also been surprisingly found that nitrogen doping of beta tantalum increases the resistivity thereof rather than decreases it.